Copper interconnect fabrication typically involves forming a damascene opening in an interlayer dielectric (ILD) followed by sequential blanket film depositions of barrier, seed, and copper fill materials. Upon removal of barrier, seed, and copper fill materials not contained within the damascene opening, the interconnect structure is formed.
Conventional methods for forming the barrier include using a physical vapor deposition (PVD) process to deposit tantalum and/or tantalum nitride within the trench opening. This approach has been effective in forming interconnect's having line widths greater than approximately 100 nanometers (nm). However below 100 nm, the barrier thickness does not scale proportionately and problems can be encountered. These problems are the result of minimum thickness limitations due to the inherent non-uniformity/non-conformality of PVD deposited films.
Continuing to reduce the barrier's thickness to accommodate interconnect scaling below 100 nm can result in barrier thinning to a point where the barrier's integrity is compromised, in which case device reliability can be a concern. On the other hand, failing to proportionately scale the barrier can result in it occupying an increasingly larger percentage of the interconnect's overall volume. In this case, since the barrier typically has a higher resistance than that of the copper seed and/or fill material, the interconnect's resistance will increase.
Barriers formed using atomic layer deposition (ALD) are an alternative to PVD barriers in scaled interconnect technology. ALD is capable of depositing thinner, more conformal, and more uniform barrier films as compared to PVD. However, depositing ALD barrier films on materials such as low dielectric constant (low-k) ILDs is feasible but not without taking precautions. This is because during deposition, ALD precursors can absorb into the ILD's bulk and then eventually outgas and create problems during subsequent patterning processes. Current methods for addressing include sealing the ILD surface before or after ALD barrier deposition/removal. However this may be impractical or undesirable because it adds processing steps and it can require the use of films which increase the ILD's overall dielectric constant.
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